Treatment of stenosis by angioplasty balloon catheters is well known. Typically a lesion can be opened by a standard balloon catheter quickly and easily at moderate inflation pressures. Some stenotic lesions can be highly resistant to opening at reasonable pressures and occasionally balloon catheters are not strong enough to sufficiently open such lesions. For example, when treating a stenosis that occurs at the venous anastomosis of a dialysis graft, it is found that often these lesions require pressure in excess of 28 atmospheres. Such a high pressure increases the degree of vascular trauma caused by the rapid stretching and tearing of the media and adventia layers of the vessel. Vascular trauma to the vessel wall has been shown to increase the ingrowth of smooth muscle cells, which is directly related to increased restenosis rates.
Despite the above drawbacks, high-pressure angioplasty balloons were developed to treat these highly resistant lesions. Typically these catheters require larger sheath sizes than low-pressure balloon catheters and are expensive due to the materials and design required to achieve high pressures.
To address the problems associated with conventional high pressure angioplasty balloons, techniques were developed in which an angioplasty balloon was placed along side of a guidewire and then inflated, creating focal pressure against the lesion along the guidewire surface. This technique became known as the Buddy Wire technique. Scientific studies have demonstrated that the application of slow, low pressure delivered in a focused manner reduces the degree of vessel trauma and thus post-procedure complications including restenosis. Although the technique is still practiced today, there are several disadvantages with the procedure. The technique typically is done with a single “Buddy Wire”, resulting in a single focal pressure line against the lesion. The use of more than one wire will address this problem but it is difficult to control the positioning within the lesion of more than one guidewire. Lack of control over guidewire location relative to the balloon makes the procedure more unpredictable and difficult than conventional angioplasty procedures.
In the early 1990s, cutting balloon catheters were developed. Barath disclosed a cutting balloon in U.S. Pat. No. 5,196,024 entitled “Balloon Catheter with Cutting Edge”, issued Mar. 23, 1993, which is incorporated herein by reference. Barath's design and other cutting angioplasty balloons have microsurgical cutting wires in the form of blades that are pre-mounted to the surface of the balloon. When the balloon is inflated the blades cut partially through the vessel wall resulting in controlled, localized dissection of the inner vessel layers. The blades produce high focal stress lines along the lesion surface in a controlled, predictable manner. Because the pressure is concentrated along the blades, less balloon inflation pressure is required to open the stenosis. For example, a lesion that may require 30 atms with standard high pressure angioplasty may open at approximately 8 atms with a cutting balloon device.
Although cutting balloon technology addresses some of the problems associated with conventional angioplasty, there are several drawbacks with the use of cutting balloons. The cutting blades or wires increase the overall profile of the angioplasty device. Specifically, a cutting balloon profile is larger than a conventional Percutaneous Transluminal Coronary Angioplasty (PTCA) or Percutaneous Transluminal Angioplasty (PTA) catheter with the same nominal inflated diameter. Thus, the catheter requires a larger insertion sheath than a standard angioplasty balloon. Difficulties in advancing the balloon through the vasculature to the target lesion are more frequent with a cutting balloon than with a conventional angioplasty balloon of an equivalent inflation diameter due to the larger profile.
Insertion, advancement and placement of cutting balloons are also more difficult because the relatively stiff blade materials prevent the cutting balloon from being as flexible as standard angioplasty catheters. Accordingly, tracking the device through tortuous vasculature is more problematic with the cutting balloon. To increase the flexibility, one conventional catheter incorporated keyhole cutouts in the blades. While the keyhole design increases the overall flexibility of the cutting balloon, it adds complexity to the micro-precision manufacturing process and costs. Radisch attempts to address the blade stiffness problem in his U.S. Patent Application No. 2003/0040770 entitled “Segmented Balloon Catheter Blade”, which is incorporated herein by reference. Radisch's design utilizes individual blade segments attached to a base in such a manner as to allow relative movement between adjacent blade segment, thereby providing increased flexibility. Again, while increasing flexibility, the design adds complexity to the manufacturing cost and still does not address the problems associated with increased overall device diameter.
Prior art cutting balloons are also disadvantageous during withdrawal of the device. Some cutting balloon designs use the balloon creases to cover and protect the vessel wall from unintentional incising during withdrawal. One such design is disclosed in U.S. Pat. No. 5,320,634 entitled “Balloon Catheter with Seated Cutting Edges”, issued Jun. 14, 1994 to Vigil, which is incorporated herein by reference. While Vigil provides an increased level of protection during withdrawal, there are still disadvantages with the Vigil design. The balloon deflation process is not always controllable and the deflated balloon surface does not always adequately cover the blades. Furthermore, deflation failures, common with angioplasty balloons, may result in significant patient complications when the cutting balloon fails to completely deflate. Unintentional vessel dissection may occur during withdrawal. Balloon rupture and other mechanical failure may result in the necessity of surgically retrieving blade components from the vessel.
Another disadvantage of cutting balloons is cost. The cutting balloons cost approximately four times the cost of a standard balloon catheter. Consequently the cutting balloon catheter is only used when standard angioplasty balloons fail to open a lesion. Even so, the medical facility needs to carry a complete inventory of both standard and cutting balloons in order to be prepared to treat various size lesions. This becomes very expensive and requires a large inventory space. Barath attempts to overcome this problem in U.S. Pat. No. 5,797,935 entitled “Balloon Activated Forced Concentrators for Incising Stenotic Segments”, issued Aug. 25, 1998, which is incorporated herein by reference. He discloses the use of a separate “activated force concentrator” component that is mounted over a standard angioplasty balloon prior to insertion.
Although Barath's device allows customization of a standard angioplasty balloon for a variety of procedures and thus reduces inventory requirements, it does have several deficiencies. The concentrator is user-mounted on the balloon prior to insertion into the patient. The concentrator increases the overall profile of the device resulting in insertion and advancement complications as previously discussed. Even after deflation in its reduced profile, the atherotomes or blades remain exposed and may thus increase the possibility of unintentional incision of non-target vessel segments during withdrawal. Another disadvantage of Barath's concentrator design relates to balloon inventory-stocking levels. Although Barath's design reduces the inventory requirements for angioplasty procedures, each balloon length would require a separate concentrator length thus introducing complexity and additional inventory parts into the angiosuite. In addition, the difference in balloon specifications among manufacturers makes custom fitting of the concentrator to the balloon difficult.
Still another disadvantage of cutting balloons is that a physician is required to remove the standard angioplasty catheter already in the vessel and insert in its place the cutting balloon catheter. In general, cutting balloons are intended for use only after conventional angioplasty has failed to successfully restore vessel lumen patency. When that happens, the conventional angioplasty balloon is removed and then the cutting balloon is inserted and advanced to the lesion. With Barath's design, the angioplasty balloon is removed, the concentrator is mounted on the balloon, and then the concentrator-mounted balloon is re-inserted into the vessel. With either approach, the balloon exchanges carry added risk, add time to the procedure, and increase treatment costs due to additional device use.
In addition to replacing the standard catheter with a cutting balloon catheter, often it may be necessary to also replace the guidewire as well. This is because a standard angioplasty balloon may require a 0.035″ guidewire, while a cutting balloon catheter may require a smaller diameter 0.018″ or 0.014″ guidewire. As persons of ordinary skill in the art can appreciate, this procedure carries substantial added risk to the patient, not to mention the increased cost and added procedure time.
Therefore, it is desirable to provide a device and method, which can be used to convert a conventional angioplasty balloon catheter into a cutting balloon catheter without increasing the balloon diameter and without requiring an exchange or re-insertion of the catheter.
It is also desirable to provide such a device and method in which a single unit can accommodate multiple conventional angioplasty balloons of varying diameters and lengths.
It is also desirable to provide such a device and method, which provides protection of the vessel wall from the cutting elements during insertion and withdrawal of the device.
It is also desirable to provide a reliable, inexpensive, efficient and fast method of opening a stenotic lesion that fails to open using conventional angioplasty by converting an already in place angioplasty balloon to a cutting instrument.
It is also desirable to provide such a device and method which substantially reduces the requirement of carrying a complete inventory of both standard and cutting balloons in order to be prepared to treat various size lesions.